@patdet ya its 40 min one way....explain pls
distance A to B = d
speed = x
stream speed = s
d/(x + s) = 0.5
d/(x - s) = 1
x = 3d/2
time = d/x = 2/3 hr = 40min
@vishcat
Shld be 40 mins 4 a single journey..
Let D be the distance in between A n B..v= speed of the boat n u=speed of the stream/river..
Thus, D/(v+u) = 1/2...(i) n D/(v-u)= 1...(ii)
Now, From(i) n (ii), we have, v=3u..(iii)
Thus, Time taken by the boat to travel from A to B n B to A if the flow of the river ceases=D/(v - v /3) = 3D/2v = 1 [From Eqn (ii)]
=>D/v = 40 Mins..
Thus, For a round trip, it shld be 80 Mins..
@vishcat said:hey guys an upstream-downstream problem--majhi is travelling from A to B and B to A on a boat.60 min to go from A to B & 30 min from B to A.what would be the time taken by the boat if the flow of the river ceases???
40 mins?
speed of boat = u
speed of stream = x
D/(u - x) = 60
D/(u + x) = 30
solving this will get----> u = 3x
D/(u + u/3) = 30
3D/(4u) = 30
D/u = 40 mins
@vishcat said:hey guys an upstream-downstream problem--majhi is travelling from A to B and B to A on a boat.60 min to go from A to B & 30 min from B to A.what would be the time taken by the boat if the flow of the river ceases???
40..
river flow will be 1/3 of boat normal speed
(r+s)*t/s will give the ans where s--> river flow, t--> time taken in flow of river
river flow will be 1/3 of boat normal speed
(r+s)*t/s will give the ans where s--> river flow, t--> time taken in flow of river
@pyashraj thanks for a very detailed explanation....i think everybody should clear everybody's doubt in the same way......but is substituting in one of those equations the only way to solve this?? i was hoping that i get a short cut with the concept behind it
@vishcat
Well the concept is pretty simple..its based on relative speed..i dnt thnk there is any shrtcut 4 sch a prmblm..u've 2 establish few ground Eqn's..n then solve accrdngly..U can even check few soln that other puys have given.. :)
@vishcat said:@negiSannupls elaborate..was that a shortcut that u mentioned?
I just used the equation to establish the relation between river flow and boat speed.
I don think there is a short for this.
I don think there is a short for this.
What is the remainder when 1! + 2 × 2! + 3 × 3! + 4 × 4! + … + 12 × 12! is divided by 13?
1) 1
2) 12
3) 11
4) 0
I got it as 1) 1, the OA is 2) 12....I want to know why?
My approach:
n*n! = (n+1-1)*n! = (n+1)! - n!
So 13!-12! remains.
12!/13 = -1
hence the remainder is +1.
1) 1
2) 12
3) 11
4) 0
I got it as 1) 1, the OA is 2) 12....I want to know why?
My approach:
n*n! = (n+1-1)*n! = (n+1)! - n!
So 13!-12! remains.
12!/13 = -1
hence the remainder is +1.
@DreamOvrReality said:What is the remainder when 1! + 2 × 2! + 3 × 3! + 4 × 4! + … + 12 × 12! is divided by 13?1) 12) 123) 114) 0I got it as 1) 1, the OA is 2) 12....I want to know why?My approach:n*n! = (n+1-1)*n! = (n+1)! - n!So 13!-12! remains.12!/13 = -1hence the remainder is +1.
1! + 2 × 2! + 3 × 3! + 4 × 4! + … + 12 × 12!
=(2-1)1! + (3-1)2! + (4-1)3!...............(13-1)12!
=2!- 1!+3!-2!+4!-3!..................13!-12!
=13! - 1!
REMAINDER I S -1
OR 12
@DreamOvrReality said:What is the remainder when 1! + 2 × 2! + 3 × 3! + 4 × 4! + … + 12 × 12! is divided by 13?1) 12) 123) 114) 0I got it as 1) 1, the OA is 2) 12....I want to know why?My approach:n*n! = (n+1-1)*n! = (n+1)! - n!So 13!-12! remains.12!/13 = -1hence the remainder is +1.
Your approach is absolutely fine, just that it would be 13!-1! and not 13!-12!. On careful observation you would realize that yourself I guess. 
aaj maamla itna sust kyun hai yahan parr? 
@adityaknsit said:Your approach is absolutely fine, just that it would be 13!-1! and not 13!-12!. On careful observation you would realize that yourself I guess.
Yup, my best buddy (read careless mistake) makes a grand entrance here!!!
need to be more vigil !!!!
Post karo questions, solve kartain hain. I might be posting some more questions, to discuss....
need to be more vigil !!!!
Post karo questions, solve kartain hain. I might be posting some more questions, to discuss....
What is the highest possible value of 'n' for which 3^(1024) – 1 is divisible by 2^n?
1) 13
2) 10
3) 11
4) 12
1) 13
2) 10
3) 11
4) 12
(4-1)^1024 - 1
.........- c(1024,1023)4 + 1 -1
............. - 4*1024
---------- - 2^12
so highest ower of 2 is 12
@DreamOvrReality said:What is the highest possible value of 'n' for which 3^(1024) – 1 is divisible by 2^n?1) 132) 103) 114) 12
@DreamOvrReality said:What is the highest possible value of 'n' for which 3^(1024) – 1 is divisible by 2^n?1) 132) 103) 114) 12
c?
(3^1024)-1 =(2+1)^1024-1
=1+2*(1024C1)+2^2*(1024C2)...............- 1.........
now all will contain at least 1024*2= 2^11...........
=1+2*(1024C1)+2^2*(1024C2)...............- 1.........
now all will contain at least 1024*2= 2^11...........
@adityaknsit said:c?
The OA is d)12
@rkshtsurana said:(4-1)^1024 - 1.........- c(1024,1023)4 + 1 -1............. - 4*1024---------- - 2^12so highest ower of 2 is 12
Interesting approach
Euler's theorem didn't help here.
I used Euler's Theorem here and got 11 which is not the correct answer.
3^1024-1 would be divisible by 2^11
Euler's theorem didn't help here.
I used Euler's Theorem here and got 11 which is not the correct answer.
3^1024-1 would be divisible by 2^11